Mei was somewhat active before everything went Dive. Once Dive is weakened a bit so less mobile heroes are viable, she should re-enter the fray.
Junkrat imo can recieve a few sensible buffs that in no way would overpower him, like laying down more traps and giving his terrible ult more health so it can survive to hit anyone.
Likewise, Torbjorn could get a couple sensible buffs that wouldn't overpower him either that are nicely outlined
here. Edit: for some reason, that thread got 404'd. Um, basically what it suggested was to fix the headbox (becuase it's twice as large as his head right now), buff the speed in which he sets up his turrets so he can be more mobile in a game where that's very important, and make it so that the turret doesn't autotarget people behind a shield when there are other targets out in the open.
Bastion they already reworked pretty substantially and I think he's in a similar area to Mei where Dive is just too strong and he'd be more viable once it dies down.
Widowmaker imo could use a fundamental rework. She's not over or underpowered, but the fact is that sniping is all she can do. If you can point and click, you get the kill and if you can't, you don't. Some people like the purity of that, but I think it just makes her uninteresting to play. She needs this rework on consoles more than PC, because console players either cheat with the M/KB or just don't have the accuracy needed to be useful.
Hanzo is straight up fine as is. I don't want him to be Roadhogged.